1-2-3 Inning

What is 1-2-3 Inning?

An inning of play in which the offensive team is retired by three straight outs without any of the batters reaching the bases. This can include strikeouts by the pitcher as well as putouts by the fielders.

Sporting Charts explains 1-2-3 Inning

A 1-2-3 inning only occurs when no batter reaches the base. For example, if in an inning a batter gets on base and a hitter bats into a double play followed by a strikeout or putout for the third batter, it doesn't count as a 1-2-3 inning, even though there were only three batters for the offense.